The present invention relates to analysis of polymer resins. In particular, the invention relates to determination of polymer molecular weight.
Early methods for the determination of polymer molecular weight relied on chromatographic separation and comparison to polymer standards with narrow, known molecular weight distributions. These methods were very slow and subject to large experimental errors.
The use of light scattering methods for polymer characterization, in pioneered by Zimm (see, for example, Journal of Chemical Physics, volume 16, number 12, pages 1099-1116 (1948)), offered the advantage of absolute determination of molar mass. Light scattering methods have been used in static and flow analysis systems for characterization of polymer solutions without separation, but these measurements are unsuitable for analysis of polymerization reaction mixtures because the presence of low molecular weight reactants, products, and catalysts interferes with the accurate determination of average molecular weight for the polymeric component of the reaction mixture.
When paired with size exclusion chromatography and a concentration detection method such as differential refractive index, light scattering detection enables precise characterization of the molecular weight distribution of polydisperse polymer samples. See, for example, P. J. Wyatt, Analytica Chimica Acta, volume 272, pages 1-40 (1993). However, known methods combining chromatographic separation and light-scattering detection require several minutes for analysis of each sample.
When modern combinatorial methods are used to screen polymerization reaction conditions or catalyst materials, there is often a desire to determine the average molecular weight of the product polymer. However, the large number of samples generated by combinatorial methods can easily overwhelm the traditional analyses described above.
There is therefore a need for an analytical method that enables rapid molecular weight determination of polymer resins, is free from interferences by small molecules, and is easily automated.